In the fields of television, radio, and the like, various types of antennas are previously developed for receiving or transmitting electromagnetic waves of picture and image signals. The known antennas include an aperture antenna such as a parabolic antenna and a reflective mirror antenna, a linear antenna such as a dipole antenna and a patch antenna, and an array antenna such as a planer antenna and a slot antenna, for example.
For such antennas, a lot of improvements are made mainly for the purposes of improving the factors of directivity, gain, impedance, and the like. The form (topology) and the location of an antenna are designed and determined so that the directivity, gain and impedance are optimized, depending on the frequency of radio wave to be transmitted/received, and the direction from which the radio wave is received.
Recently, in accordance with the developments of portable information terminals utilizing radio transmission and equipment for network (so-called wireless LAN) in personal computers, flexibility is required for the functions of antennas.
Especially in the case where a mobile instrument such as a portable information terminal is used while it is being moved, it may be difficult to carry the radio wave depending on the location, and the power of transmission/reception signals may be weak. Thus, the S/N ratio of the signals may disadvantageously be reduced. In connection with the increase in frequency of electromagnetic waves, a probability that the electromagnetic waves are reflected from an obstruction, thereby causing a so-called multi-pass is increased, and the accuracy of radio communication is degraded.
For the above-described reasons, we require an antenna which can maintain good transmission/receiving characteristics by adapting to any possible change in communication conditions. As the frequency of a signal becomes higher, the directivity of radio wave becomes stronger. Thus, in the case where a number of wireless terminals exist in a communication range, an antenna is required to have a function of realizing communication through a path (an optimum radio path) for effectively communicating with a wireless terminal to be connected.
However, in a conventional antenna, the form of the antenna is fixed, so that the characteristics of the antenna is substantially uniformly determined depending on the predetermined form. Therefore, it is difficult to maintain good transmission/receiving characteristics by adapting to the change in communication conditions. Especially in the case where the frequency of the electromagnetic waves to be handled, and the incident direction of electromagnetic waves are changed, it is difficult to change the antenna characteristics by following the changed conditions.
A main object of the present invention is to provide an antenna capable of dynamically changing the form of an antenna element so as to optimize the parameters of a directivity characteristic, a gain characteristic, an impedance characteristic, and the like of the antenna.
Another object of the present invention is to provide an apparatus provided with such an antenna.
Still another object of the present invention is to provide a producing method and a designing method of an antenna which can determine an optimum form in given conditions by dynamically changing the form of an antenna element.